a. Definition of Terms
All references to periods and groups within the periodic table of elements are based on the format of the periodic table adopted by the American Chemical Society and published in the Chemical and Engineering News, Feb. 4, 1985, p. 26. In this form the prior numbering of the periods was retained, but the Roman numeral numbering of groups and the A and B group designations (having opposite meanings in the U.S. and Europe) were replaced by a simple left to right 1 through 18 numbering of the groups.
The term "dopant" is employed herein to designate any element or ion other than silver or halide incorporated in a face centered silver halide crystal lattice.
The term "metal" in referring to elements includes all elements other than those of the following atomic numbers: 2, 5-10, 14-18, 33-36, 52-54, 85 and 86.
The term "Group VIII metal" refers to an element from period 4, 5 or 6 and any one of groups 8 to 10 inclusive.
The term "Group VIII noble metal" refers to an element from period 5 or 6 and any one of groups 8 to 10 inclusive.
The term "palladium triad metal" refers to an element from period 5 and any one of groups 8 to 10 inclusive.
The term "platinum triad metal" refers to an element from period 6 and any one of groups 8 to 10 inclusive.
The term "halide" is employed in its conventional usage in silver halide photography to indicate chloride, bromide or iodide.
The term "pseudohalide" refers to groups known to approximate the properties of halides--that is, monovalent anionic groups sufficiently electronegative to exhibit a positive Hammett sigma value at least equaling that of a halide--e.g., CN.sup.--, OCN.sup.--, SCN.sup.--, SeCN.sup.--, TeCN.sup.--, N.sub.3.sup.--, C(CN).sub.3.sup.-- and CH.sup.--.
The term "C--C, H--C or C--N--H organic" refers to groups that contain at least one carbon-to-carbon bond, at least one carbon-to-hydrogen bond or at least one carbon-to-nitrogen-to-hydrogen bond sequence.
To avoid repetition, it is understood that all references to photographic emulsions are to negative-working photographic emulsions, except as otherwise indicated.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England.
b. Prior Art
Research Disclosure, Vol. 176, December 1978, Item 17643, Section I, sub-section A, states that "sensitizing compounds, such as compounds of copper, thallium, lead, bismuth, cadmium and Group VIII noble metals, can be present during precipitation of silver halide" emulsions. The quoted passage is followed by citations to demonstrate the general knowledge of the art that metals incorporated as dopants in silver halide grains during precipitation are capable of acting to improve grain sensitivity.
Research Disclosure, Vol. 308, December 1989, Item 308119, Section I, sub-section D, states that "compounds of metals such as copper, thallium, lead, mercury, bismuth, zinc, cadmium, rhenium, and Group VIII metals (e.g., iron, ruthenium, rhodium, palladium, osmium, iridium and platinum) can be present during the precipitation of silver halide" emulsions. The quoted passage is essentially cumulative with Research Disclosure 17643, Section I, sub-section A, except that the metals have been broadened beyond sensitizers to include those that otherwise modify photographic performance when included as dopants during silver halide precipitation.
Research Disclosure 308119, sub-section D, proceeds further to point out a fundamental change that occurred in the art between the 1978 and 1989 publication dates of these silver halide photography surveys. Research Disclosure 308118, I-D states further:
The metals introduced during grain nucleation and/or growth can enter the grains as dopants to modify photographic properties, depending on their level and location within the grains. When the metal forms a past of a coordination complex, such as a hexacoordination complex or a tetracoordination complex, the ligands can also be occluded within the grains. Coordination ligands, such as halo, aguo, cyano, cyanate, thiocyanate, nitrosyl, thionitrosyl, oxo, and carbonyl ligands are contemplated and can be relied upon to vary emulsion properties further.
Although it was known for many years that the photographic performance of silver halide emulsions can be modified by the introduction of dopant metal ions during grain precipitation, it was generally assumed that the anion paired with the metal ion, except when it happened to be a halide ion, did not enter the grain structure and that the counterion selection was unrelated to photographic performance. Janusonis et al U.S. Pat. No. 4,835,093; McDugle et al U.S. Pat. Nos. 4,933,272, 4,981,781 and 5,037,732; Marchetti et al U.S. Pat. No. 4,937,180; and Keevert et al U.S. Pat. No. 4,945,035 were the first to demonstrate that ligands capable of forming coordination complexes with dopant metal ions are capable of entering the grain crystal structure and producing modifications of photographic performance that are not realized by incorporation of the transition metal ion alone. In each of these patents emphasis is placed on the fact that the coordination complex steric configuration allows the metal ion in the complex to replace a silver ion in the crystal lattice with the ligands replacing adjacent halide ions.
Thereafter, by hindsight, it was realized that earlier disclosures of the addition of dopant metal ions, either as simple salts or as coordination complexes, had inadvertently disclosed useful ligand incorporations. Of these inadvertent teachings, the incorporation of iron hexacyanide during grain precipitation is the most notable and is illustrated by Shiba et al U.S. Pat. No. 3,790,390; Ohkubo et al U.S. Pat. No. 3,890,154; Iwaosa et al U.S. Pat. No. 3,901,711 and Habu et al U.S. Pat. No. 4,173,483.
Ohya et al European patent application 0 513 748 A1, published Nov. 19, 1992, discloses photographic silver halide emulsions precipitated in the presence of a metal complex having an oxidation potential of from -1.34 V to +1.66 V and a reduction potential not higher than -1.34 V and chemically sensitized in the presence of a gold-containing compound. On page 2 of the patent a table of illustrative complexes satisfying the oxidation and reduction potentials are listed. This listing includes, in addition to the complexes consisting of halide and pseudohalide ligands, K.sub.2 [Fe(EDTA)], where EDTA is an acronym for ethylenediaminetetraacetic acid. In a preferred variation it is taught to employ in combination with a required metal complex an iridium containing compound. Examples of useful iridium compounds include, in addition to simple halide salts and coordination complexes containing halide ligands, hexaamine iridium (III) salt (i.e., a [(NH.sub.3).sub.6 Ir].sup.+3 salt), hexaamine iridium (IV) salt (i.e., a [(NH.sub.3).sub.6 Ir].sup.+4 salt), a trioxalate iridium (III) salt and a trioxalate iridium (IV) salt. While offering a somewhat broader selection of ligands for use with the metals disclosed, Ohya et al does not attach any importance to ligand selection and does not address whether ligands are or are not incorporated into the grain structures during precipitation.
Ohkubo et al U.S. Pat. No. 3,672,901 (hereinafter designated Ohkubo et al '901) discloses silver halide precipitation in the presence of iron compounds. Ohkubo et al states, "Specific examples include: ferrous arsenate, ferrous bromide, ferrous carbonate, ferrous chloride, ferrous citrate, ferrous fluoride, ferrous formate, ferrous gluconate, ferrous hydroxide, ferrous iodide, ferrous lactate, ferrous oxalate, ferrous phosphate, ferrous succinate, ferrous sulfate, ferrous thiocyanate, ferrous nitrate, ammonium ferrous sulfate, potassium hexacyanoferrate (II), potassium pentacyanoamine-ferrate (II), basic ferric acetate, ferric albuminate, ammonium ferric acetate, ferric bromide, ferric chloride, ferric chromate, ferric citrate, ferric fluoride, ferric formate, ferric glycero phosphate, ferric hydroxide, acidic ferric phosphate, sodium ferric ethylenedinitrilotetraacetate, sodium ferric pyrophosphate, ferric thiocyanate, ferric sulfate, ammonium ferric sulfate, guanidine ferric sulfate, ammonium ferric citrate, potassium hexacyanoferrate (III), tris(dipyridyl) iron (III) chloride, potassium ferric pentacyanonitrosyl, and hexaurea iron (III) chloride. The only compounds reported in the Examples are hexacyanoferrate (II) and (III) and ferric thiocyanate.
Hayashi U.S. Pat. No. 5,112,732 discloses useful results to be obtained in internal latent image forming direct positive emulsions precipitated in the presence of potassoium ferrocyanide, potassium ferricyanide or an EDTA iron complex salt. Doping with iron oxalate is demonstrated to be ineffective.
While the art has heretofore achieved useful photographic performance modifications through adding dopant metal salts and coordination complexes during grain precipitation, the photographic effects that have heretofore been achieved have been attributable to the dopant metal alone or to the metal dopant in combination with coordination complex ligands chosen from only a few restricted categories: halo, pseudohalo, aguo, nitrosyl, thionitrosyl, carbonyl and oxo ligands.
Prior to the present invention reported introductions during grain precipitation of metal coordination complexes containing organic ligands have not demonstrated photographically useful modifying effects attributable to the presence of the organic ligands, and, in fact, such coordination complexes have limited the photographic modifications that would be expected from introducing the metal in the form of a simple salt. Performance modification failures employing ethylenediamine and trioxalate metal coordination complexes of types analogous to those suggested by Ohya et al and Ohkubo et al '901 are presented below as comparative Examples.